Electroluminescent filament

ABSTRACT

An electroluminescent filament of at least two wires made of electrical conductors each having an electrically insulating covering over the surface is provided. The wires are placed in abutment and covered with a phosphorescent material and the total thickness of the filament is controlled. Helically wound wires are used wherein the distance between the helical loop centers is controlled for best performance.

United States Patent 1191 Hosford June 25, 1974 5 ELECTROLUMINESCENTFILAMENT 3.069579 12/1962 Berg et al. 3 l3/l08 A [76] Inve to onzo L o o30 S 3,571,647 3/l97l Robinson 3l3/l08 A Brentwood Dr., Moorestown, NJ.1 08057 Primary Exammer-James W. Lawrence Assistant ExaminerWm. H.Punter [22] Filed: Nov. 2, 1972 Attorney, Agent, or Firm-Thomas A.Lennox, Esq. [21] Appl. No.: 303,101

[57] ABSTRACT 521 US. Cl. ..313/498, 313/345- electroluminescentfilament of at least two Wires [51] Int. Cl. .lj.'.;.'....l.ii65323 madeof electrical conductors each having electri- [58] n w of Search 313/108A, 108 R, 92 p cally insulating covering over the surface is provided.313/108 B, 344445; 250/225 The wires are placed in abutment and coveredwith a phosphorescent material and the total thickness of the [56]References Cited filament is controlled. Helically wound wires are usedUNITED STATES PATENTS wherein the distance between the helical loopcenters 2 684 450 7/1954 Mager at al 313/108 A is controlled for bestperformance. 1052:1212 9/1962 Dow 313/108 A 12 Claims, 3 Drawing FiguresELECTROLUMINESCENT FILAMENT BACKGROUND OF INVENTION Manyelectroluminescent devices have been proposed, but few, if any, haveproved a sufficiently effective light source for mass commercialmarketing. Deficiencies include low efficiency of light output, shortlife, inability to color the light effectively and pennanently, lowcapacity, inapplicable to low cost continuous production, and others.

Electroluminescent phosphors exhibit luminescence in the presence ofelectric fields. While it is known that higher voltage and/or higherfrequency of alternating current yields higher brightness, these inputsseriously reduce the life of the electroluminescent device. In commonpractice, the electric fields are generated by alternating current whichmay be either a direct field or a fringing field. Therefore, it is mostdesirable to construct a filament which could be used alone or combinedwith other filaments to make strands which would provide efficient lightoutput and long life at moderate voltage and frequencies, such asordinary house current.

The present invention relates to an electroluminescent filament thatuses a fringing electric field surrounding at least two electricalconductors separated by an electrical insulator. A phosphor is appliedto the outer surface of the wires and caused to luminesce by anelectrical current applied across the conductors.

Prior art devices have been described of this general type such as inU.S. Pat. No. 2,684,450 to E. L. Mager, et al., July 20, 1954, whereinconductors were wrapped around an insulator, covered with phosphor.Also, in U.S. Pat. No. 3,052,812 to F. w. Dow, Sept. 4, 1962, whereintwo wires were wound in various configurations to form relatively largediameter strands, generally with only one wire insulated. Also, in U.S.Pat. No. 3,571,647 to Bessie A. Robinson, Mar. 23, 1971, insulated wireswere twisted together without details. Attempts to construct thesedevices either provided filaments that fail almost immediately or yieldan almost imperceptible glow under conditions that yield a reasonablelife.

A particular difficulty arises from the use of commercially availablewire, such as magnet wire, in that the surface of the smaller gauge wirehas relatively large raised imperfections, which, when coated with adielectric, provide points of weakness in the insulation and limit thelife or performance of an electroluminescent device constructed fromthem. These hot spots on the surface make all prior electroluminescentdevices using insulation on only one wire, essentially useless.

SUMMARY OF INVENTION More particularly, this invention relates toelectroluminescent devices offering high brightness and efficiency atthe voltage and alternating cycle chosen, a more efficient capacitancethan prior devices, and extremely long service life. Further, thisinvention relates to electroluminescent devices which provideversatility and efficiency in allowing the inclusion of permanent colorbodies into the phosphor. Further, the electroluminescent devices areextremely ductle and durable as compared to prior devices.

It is an object of my invention to provide an electroluminescentfilament that has increased brightness at relatively low voltage andfrequency and that can be commercially reliable without failing due toarcing between the conductors. It is a further object that the filamentbe able to be produced by continuous methods with reliability suitablefor consumer use. It is the object that the filament be able to beformed, twisted or wound to fonn designs, such as signs, crafts andarts, digital readouts, and indicators of an ornate or decorativenature. It is also intended that the filaments be grouped to provide ahigher light output for illumination of the object on which thefilaments are attached, such as interior emergency lighting on fixtures,baseboards and the like.

Therefore, my invention is an electroluminescent filament of at leasttwo wires with each wire being an electrical conductor covered with anelectrical insulator on its surface. The wires are placed in an abuttingrelation along their length and a phosphor coating applied to bothwires. The total thickness of the filament is less than 10 mils.

It should be realized that by using the term abutting it is intended toindicate that the insulation of the wires touch. However, in anembodiment of the invention, where wire is helically wound around otherwire, the looping wire touches the relatively straight wire, but theadjacent loops of the helical coil are preferably spaced a certaindistance apart. When the embodiment of the invention employs two or morerelatively parallel wires, their insulation touches for greatestefficiency.

DESCRIPTION OF PREFERRED EMBODIMENTS For the purpose of illustrating theinvention, drawings and specific descriptions are provided, although itshould be understood that the invention is not limited to these specificembodiments.

FIG. 1 illustrates an embodiment of the present invention.

FIG. 2 is a perspective view of a second embodiment of the invention.

FIG. 3 is a transverse sectional view of the embodiment of FIG. 2.

I have found that the total thickness of the filament is critical toperformance. The thickness is required to be less than 10 mils, and bestperformance is obtained if the total thickness is 8 mils or less. Thereis no minimum thickness until there is insufficient conductive materialin the wire to carry the current required to excite the phosphor. Thepresent state of the art limits the total thickness of the filamentsince copper wire presently produced less than about 2 mils in thicknessis generally insufficient to efficiently carry the current and providelong life to the filament. Therefore, the use of copper presently limitsthe thickness of the filament to greater than about 4 mils dependingupon the configuration of the filament. Of course, other more conductivematerial will allow thinner filaments.

As stated above, the wires are placed in an abutting relationship. Whentwo or more wires are placed in parallel, it is necessary that theytouch. However, as stated above, when wires are helically wound aroundrelatively straight wire, it is preferred that the helically wound loopsnot touch. In fact, I have discovered that a specific pitch between theloops provides particularly efficient illumination. This pitch isdependent somewhat upon the total thickness of the filament, but iswithin the range of about 5 to 12 mils. The pitch is preferablycontrolled in the range of 6 to l0 mils. Most preferred filaments areobtained by controlling the pitch to the range of 7 to 9 mils. Thispitch distance is measured between loops of the same wire or betweenloops of different wires in multi-loop constructions.

This invention is not limited to the number of wires in the constructionand may include any number of essentially parallel wires and any numberof helically wound wires wound around parallel, twisted or helicalwires. The wires may be of differing colors and may be connected inpairs or groups to achieve various effects.

Considering the drawings in detail, there is shown in FIG. I, anelectroluminescent filament designated 10. In this embodiment wire 11consisting of copper conductor l2 and polymeric electrical insulator 13and wire 15 consisting of copper conductor 16 and polymeric electricalinsulator 17 are laid in abutment in a roughly parallel configuration.The wires may be twisted, intertwined or even entangled togetherdepending on the effect desired as long as they are in abutment. Aphosphor 20 is located primarily in the crevices between wires 11 and 15but also to a lesser degree over the entire surface of the wires. Alight transparent or at least highly translucent polymeric coating 21covers and protects the entire filament from damage due to hard use.

A preferred embodiment is depicted in FIGS. 2 and 3 of anelectroluminescent filament designated 10. It includes wire 11'helically wound around wire The wire 11 is shown the same size as wire15' but this is not necessary even within this preferred embodiment. Itshould be understood that the wires can be of the same size or thestraight wire can be larger or smaller than the helical wire ifmanufacturing procedures permit. Wire 11 consists of a copper conductor12 covered with an insulator 13'. The insulator I3 is a dielectricmaterial such as enamel or Paralyne C and N as disclosed below. The wallof the insulator 13' should be as thin as possible in accordance withthe principles set forth below. Although the conductor 16 is illustratedas having a round cross section, the conductor and indeed the entirewire 15' can be square, rectangular or any shape in cross section asdesired. The wire 15' includes a conductor 16' and an insulator 17'. Theconductor 16 is preferably smaller in cross-sectional dimension than theconductor 12 so that it can be more readily would about it. However,this is not a necessary requirement. Otherwise, the conductor 16' is thesame as the conductor 12. The insulator 17' is the same as the insulator13', but may, of course, be of different thickness.

In FIG. 2, the coils of the wire 11' are shown spaced apart. Thisdistance apart 25 between the coils as measured from wire center to wirecenter is referred to herein as the pitch." As stated above it ispreferred that this distance be in the range of'6 to 12 mils.

The wires 11 and 15' are covered with a powdered phosphor material 20'mixed with an appropriate polymeric binder such as thermoplastic resins,epoxy resin, and the like, to make the phosphor adhere to the insulatingcoating on the wires 11 and 15. The phosphor coating is placed over andmostly between the wires to the extent possible. The phosphor may, forexample, include any one of the following or a mixture thereof:

1. Sylvania Type 523 phosphor consisting of zinc sulfide and manganesewhich generates a yellow color at 60, 400 and 6,000 Hz with a peakwavelength of 580 nm and has Fisher sub-sieve sizer number of 19.4.

2. Sylvania Type 723 phosphor consisting of zinc sulfide and copperwhich generates a green color at 60 Hz, bluegreen at 400 Hz, and blue at6,000 Hz with a peak wavelength of 497 nm and has Fisher sub-sieve sizernumber of 20.0.

3. Sylvania Type 814 phosphor consisting of zinc sulfide and copperwhich generates a blue color at 60, 400 and 6,000 Hz with a peakwavelength of 452 nm and has a Fisher sub-sieve sizer number of 24.0.

Each of the above phosphors is available from the Sylvania Division ofGeneral Telephone and Electronics. Of course, other phosphors availableon the market can be substituted for those disclosed above. If desired,fluorescent materials can be added to the phosphor to give it color inits unexcited states; that is, in ambient light. Such fluorescentmaterials may include fluores- 7 cent paints available on the market.One such fluorescent paint in varying colors is available from theIllinois Bronze Powder and Paint Co., Lake Zurich, Ill. and sold underthe trademark DAZ-L.

If desired, wires 11' and 15 together with the phosphor material 20 maybe enclosed within a coating of light transparent material such as aflexible polymeric. The coating permits the light to be emitted by thefilament 10' while at the same time protecting the phosphor coating. Thetransparent coating may contain color bodies in the form of dye ortranslucent particles.

In accordance with known principles of electroluminescence, filaments 10and 10' are energized by connecting a voltage source to the conductors.Such voltage source may, for example, be an alternating current at 60 Hzand the voltage at or 220 volts. A fringe electric field is developedthat excites the phosphors to luminesce.

An example of a filament 10' which produces an enhanced luminescenceconsists of the following:

Wire 15' includes a No. 44, 2 mil, copper wire having an 0.05 mil enamelinsulating coating. The wire 11' is also a No. 44 copper conductor withan 0.05 mil insulator coating. The wire 11 is would on the wire 15 atthe density of turns per inch for a pitch of 8 mils to yield an overalldiameter of the filament of 6 mils as desired. Measurements indicatethat such a wire yields more than 0.4 foot lambert when excited with a110 volt alternatingcurrent at 60 Hz..There is a substantial increase inbrightness at 220 volts and 60 Hz since the brightness in foot lambertsis proportional to the square of the voltage. Experiments with knownelectroluminescent filaments produce substantially lower brightnesslevels.

In the example described above, the insulatordielectric for the wires 1l and 15' is enamel. If desired, the insulator could be Parylene C and Ncoated on the conductors in accordance with the process available fromUnion Carbide Corporation. The advantage of using Parylene C and N isthat it reduces the size of the insulator-dietectric on the wires. Thereduction in the total thickness of the insulator-dietectric using thesame size core conductors 12' and 16, enhances the fringe field andhence the excitation of the phosphors.

Similarly, the filament 10 may be constructed using No. 40, 3 mil,copper wire with 0.1 mil coating as wire 15 while retaining No. 44insulated copper wire with an 8 mil pitch as the winding. The overallthickness of the filament is about 7 A mils and yields almost the samelight output under the same excitation as the device above.

In a third construction of the filament the core wire is No. 37 (4 ismil) copper wire with an 0.15 mil insulation, wrapped again withinsulated No. 44 wire on an 8 mil pitch to produce a filament about 9mils thick. The illumination obtained is somewhat poorer than obtainedwith the first construction.-

Similar constructions to filament 10' yield the following results:

Measurements of capacitance on filament 10' yield a C-Factor of about 86phase angle as compared to a perfect capacitor which would yield 90.This high efficiency is favorable as compared to prior filament devices.

The prior examples are merely illustrative of my invention and are notintended to limit the scope of the patent grant. My invention is limitedonly by the appended claims.

1 claim:

1. An electroluminescent filament comprising:

at least two wires,

each wire comprising an electrical conductor and an electricallyinsulating covering on the surface of the conductor,

the wires being in abutting relation along their length,

a phosphor coating overlying the wires, and

the total thickness of the filament including the insulators coveringthe conductors being less than 10 mils.

2. An electroluminescent filament in accordance with claim 1 wherein thetotal thickness of the filament is less than about 8 mils.

3. An electroluminescent filament in accordance with claim 1 wherein thetotal thickness of the filament including the phosphor coating, which isessentially all between the wires except where the wires are inabutment, is less than 10 mils.

4. An electroluminescent filament in accordance with claim 3 wherein thetotal thickness is less than 8 mils.

5. An electroluminescent filament as set forth in claim 1 wherein atleast two wires are in parallel abutting relation.

6. An electroluminescent filament in accordance with claim 1 wherein thewires are interwound each upon the other.

7. An electroluminescent filament in accordance with claim 1 wherein atleast one of the wires is helically wound around at least one of theother wires so that the wires are in abutting relation along theirlength.

8. An electroluminescent filament in accordance with claim 7 wherein thedistance between centers of each loop of helically wound wire and thenext adjacent loop of helically wound wire is in the range of about 6mils to about 12 mils.

9. An electroluminescent filament in accordance with claim 8 wherein thetotal thickness of filament is less than about 8 mils and the distancebetween centers of each loop is about 7 to about 9 mils.

10. An electroluminescent filament in accordance with claim 1 includinga light transparent coating overlying the wires and the phosphor.

11. An electroluminescent filament comprising:

at least two wires, each wire comprising an electrical conductor and anelectrically insulating coating on the surface,

at least one of the wires being helically wound around one of the otherwires so that the wires are in abutting relation along their length,

a phosphor coatingoverlying the wires,

the total thickness of the filament including the insulators coveringthe conductors and the phosphor coating being less than 10 mils, and

the distance between centers of each loop of helically wound wire andthe next adjacent loop of helically wound wire being in the range ofabout 6 mils to about 12 mils.

12. An electroluminescent filament in accordance with claim 11 whereinthe total thickness of the filament is in the range of about six toabout nine mils and the distance between helically loops is about 7 to 9mils.

1. An electroluminescent filament comprising: at least two wires, eachwire comprising an electrical conductor and an electrically insulatingcovering on the surface of the conductor, the wires being in abuttingrelation along their length, a phosphor coating overlying the wires, andthe total thickness of the filament including the insulators coveringthe conductors being less than 10 mils.
 2. An electroluminescentfilament in accordance with claim 1 wherein the total thickness of thefilament is less than about 8 mils.
 3. An electroluminescent filament inaccordance with claim 1 wherein the total thickness of the filamentincluding the phosphor coating, which is essentially all between thewires except where the wires are in abutment, is less than 10 mils. 4.An electroluminescent filament in accordance with claim 3 wherein thetotal thickness is less than 8 mils.
 5. An electroluminescent filamentas set forth in claim 1 wherein at least two wires are in parallelabutting relation.
 6. An electroluminescent filament in accordance withclaim 1 wherein the wires are interwound each upon the other.
 7. Anelectroluminescent filament in accordance with claim 1 wherein at leastone of the wires is helically wound around at least one of the otherwires so that the wires are in abutting relation along their length. 8.An electroluminescent filament in accordance with claim 7 wherein thedistance between centers of each loop of helically wound wire and thenext adjacent loop of helically wound wire is in the range of about 6mils to about 12 mils.
 9. An electroluminescent filament in accordancewith claim 8 wherein the total thickness of filament is less than about8 mils and the distance between centers of each loop is about 7 to about9 mils.
 10. An electroluminescent filament in accordance with claim 1including a light transparent coating overlying the wires and thephosphor.
 11. An electroluminescent filament comprising: at least twowires, each wire comprising an electrical conductor and an electricallyinsulating coating on the surface, at least one of the wires beinghelically wound around one of the other wires so that the wires are inabutting relation along their length, a phosphor coating overlying thewires, the total thickness of the filament including the insulatorscovering the conductors and the phosphor coating being less than 10mils, and the distance between centers of each loop of helically woundwire and the next adjacent loop of helically wound wire being in therange of about 6 mils to about 12 mils.
 12. An electroluminescentfilament in accordance with claim 11 wherein the total thickness of thefilament is in the range of about six to about nine mils and thedistance between helically loops is about 7 to 9 mils.